jQuery Multi Select Option-检查是否选择了一个选项

Question

I have a HTML Multi select box

<form action="form_action.php" method="Post">
<select name="cars[]" multiple id="select_id">
    <option value="all" id="option_id">All</option>
    <option value="volvo">Volvo</option>
    <option value="saab">Saab</option>
    <option value="opel">Opel</option>
    <option value="audi">Audi</option>
</select>
<input type="submit">
</form>

What I am trying to do is check if option "All" is selected or not in jQuery.

What I have tried is

<script>
        $(document).ready(function()
        {
            $('#option_id')
                .click(
                    function()
                    {
                        if ($("#select_id option[value='all']").length == 0) { //value does not exist so add
                            //Do something if not selected
                        }
                        else
                        {
                            //DO something if selected
                        }
                        //$("#select_id option:selected").removeAttr("selected");           //Remove
                        //$("#select_id option").attr('selected', 'selected');      //Add
                    }
                );
        });
    </script>

But it is not working.

Can anyone help me please?

Thanks in advance for helping.

Answer 1

Please do as below code

$('#option_id').click(function(){
if ($("#select_id option[value=all]:selected").length > 0){
    alert('all is selected');
}
else{
    //DO something if not selected
}
//$("#select_id option:selected").removeAttr("selected");           //Remove
//$("#select_id option").attr('selected', 'selected');      //Add
});

You can check below fiddle

Multi Select

Answer 2

You can use :selected selector for option to determine whether it is selected or not

if ($("#select_id option[value=all]:selected").length > 0){
   //all is selected
}

Answer 3

From what I can see, you're trying to detect whether it has been selected when you change the option in the <select> box, right?

Try this:

$("#select_id").change(function () {
  if ($(this).find("option:selected").val() == "all") {
    // all is selected
  } else {
    // all isn't selected
  }
});